F6 families of Gossypium hirsutum L. ✕ ‘Mexico Wild’ (a root‐knot tolerant primitive G. hirsutum from Mexico) were advanced through F10, with selection in greenhouse tests for resistance to root‐knot nematodes [Meloidogyne incognita acrita (Kofoid & White, 1919) Chitwood, 19491. A disinfected larval screening technique effectively classified 85% of the F6 families as intermediate to highly susceptible, even though they had been selected in F2 through F4 in the field for root‐knot resistance in highly infested soil. Two F10 lines, designated A623 and A61, having the highest resistance known to root‐knot in G. hirsutum, were developed. These lines were transgrassive segregates for resistance. Root‐knot resistance in the F1 generation from resistant A623 ✕ susceptible ‘Stoneville 213,’ ‘Coker 201,’ and ‘Dixie King II’ was incompletely dominant. Fusarium wilt [Fusarium oxysporum Schlecht. f. vasinfectum (Atk.) Snyd. ✕ Hans.] resistance in the above material was highly associated with root‐knot resistance. Therefore, it may be possible to breed for fusarium wilt resistance by breeding solely for high root‐knot resistance.
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Raymond L. Shepherd (1974) studied this question.